Hydrocracking catalyst and process



p the gasoline range.

H 2,873,246 Patented Feb. 10, 1959 HYDROCRACKING CATALYST AND PROCESS Rowland C. Hansford, Fullerton, and Dean Arthur Young, Whittier, Califi, assignors to Union Oil Company of California, Los Angeles, Calif a corporation of California No Drawing. Application April 18, 1955 Serial No.502,232

Claims. (Cl. 208-68) This invention relates to methods for the catalytic hydrocracking of high boiling hydrocarbon oils to produce therefrom lower boiling fractions such as gasoline. More particularly the invention concerns the use of certain catalysts for the hydrocracking, said catalysts being composed substantially exclusively of silica and titania in intimate admixture. The hydrocracking process itself consists in passing the high boiling feed stock in admixture with hydrogen over the catalyst at suitable temperatures, feed rates, pressures, etc. to eifect a substantial conversion of the high boiling hydrocarbons to materials boiling in Simultaneously, any organic sulfur and nitrogen compounds present in the feed are largely decomposed to hydrogen sulfide, ammonia and hydrocarbon fragments. Such .hydrocracking processes are often referred to as destructive hydrogenation, or hydrogenolysis, although it will become apparent from the following discussion that the process based on the catalysts of the present invention is to be sharply distinguished from conventional hydrogenolysis processes.

It is a principal object of this invention to provide efficient and selective catalysts for the hydrocracking of mineral oils, which will effect a maximum conversion to high quality gasoline-boiling range hydrocarbons, and a minimum of destructive degradation to products such as methane and coke. Anotherobject is to provide optimum process conditions for the utilization of such catalysts. A further object is to provide hydrocracking catalysts which are more economical than previously utilized catalysts. A still further object is to provide methods for eifectively desulfurizing and' denitrogenating high boiling feed stocks. A, specific object is toprovide catalysts which are effective for the hydrocracking of such highly refractory stocks as cycle oils from conventional thermal or catalytic cracking, whereby additional conversion to gasoline may be obtained. Another specific object is to provide catalysts which, in contrast to conventional hydrogenolysis catalysts, will produce gasoline hydrocarbons having even higher antiknock qualities than those produced byconventional catalytic cracking. Other objects and advantages will be apparent from the description which follows.

It is well known that the cracking of petroleum stocks, such as virgin gas oils from any type of crude oil, invariably leads to the production of a considerable proportion of a fraction which boils in the same range as the initial charge stock, but which is much more refractory toward further cracking. This is true whether the cracking process is non-catalytic or catalytic, and as a result there are definite limitations on the degree to which profitable recycling of this fraction to the cracking operation can be practiced. The effect of increased refractoriness of the unconverted portion of a cracking stock is particularly limiting in the case of catalytic cracking, so much so that only small recycle ratios are generally employed, further conversion. of the recycle stock often being effected in a subsequent thermal cracking operation. Recycling to extinction invariably results in poor selectivity polynuclear aromatics, by

of the conversion to gasoline as a result of excessive formation of carbonaceous catalyst depositsand of light hydrocarbon gases. This is also true in thermal cracking, except that instead of carbonaceous catalyst deposits 21 large amount of heavy tar-of high carbon content is formed.

The refractoriness of cracked recycle stocks is, the result, principally, of the formation of polynuclear aromatic hydrocarbons through reactions of dehydrogenation, hydrogen transfer, cracking, cyclization, or condensation. It is well known, for example, that recycle stocks from catalytic cracking have a high content of methylnaphthalenes. These may be formed by the cracking of long side-chains or of saturated rings attached to a naphthalene nucleus, by the dehydrogenation of polynuclear naphthenes or aromatic-naphthenes such as alkyltetralins, and even by the polymerization and cyclization of olefins produced from saturated hydrocarbons or alkyl side-chains. In thermal cracking, one important mechanism of polynuclear aromatic hydrocarbon formation is the condensation of diolefins with aromatics of lower ring content. In catalytic cracking, another important factor leading to apparent refractoriness is the accumulation of pyridineor quinoline-type compounds in the recycle stock. These basic nitrogen compounds exert a temporarypoisoning eifect on the acidic catalyst centers, and low conversion of the cycle stock results.

The above-noted diificulties are avoided or minimized by the process herein described. Thus, by preventing complete dehydrogenation of polynuclear naphthenes to hydrogenating at least partially the polynuclear aromatics already present in the charge stock, by preventing high olefin or diolefin content with subsequent reactions of polymerization, cyclization, or condensation, and by decomposing basic nitrogen compounds to innocuous ammonia, relatively high partial pressures of hydrogen can permit a maximum theoretical enter into the cracking at some stage, presumably in the very initial stages, though there may not necessarily be a net consumption of hydrogen. From the above discussion it will be apparent that the catalysts of the present invention may be used advantageously in the hydrocracking of virgin gas oils, whereby greater conversion to gasoline is obtained in a oncethrough operation than would be obtained in a similar once-through operation in conventional cracking processes, and also the unconverted fraction is not greatly degraded with respect to refractoriness, and may hence be recycled substantially to extinction. It will be apparent also that the catalyst may be employed to treat the refractory residues from conventional cracking operations whereby a substantial yield of high quality gasoline is obtained. The residue from this operation may likewise be recycled either to the hydrocracking step or back to a conventional cracking step in the absence of hydrogen. These results are not obtainable when treating such recycle stocks with a conventional silica-alumina catalyst; hydrogen is practically without eifect on the cracking of such stocks with this catalyst.

The hydrocracking conditions employed herein involve passing the vaporiaedhydrocarbons over the finished in such uses.

-zirconia, and silica-alumina-zirconia.

catalyst at temperatures ranging between about 750 and 1050 F., hydrogen pressures between about 500 and 5000 p. s. i. g., and space velocities ranging between about 0.1 and 10.0. The preferred hydrogen ratios may range between about 1000 and 10,000 s. c. f. per barrel of feed. The minimum hydrogen pressure of about 500 It is well-known in the art that combinations of silica.

with certain transitional or non-transitional metal oxides are useful catalysts for the pyrolysis of hydrocarbons at elevated temperatures in the absence of added hydrogen. Composites of silica and zirconia are specifically known Zirconia in fact appearsto be the only transitional metal oxide which is known to form an active cracking catalyst with silica. However, none of these silica composites has been regarded as possessing any significant hydrogenating activity.

It is generally believed that cracking catalysts owe their activity to the presence of acidic centers on the catalyst surface, since it is known that active cracking catalysts exhibit acidic properties and that many of the reactions which occur in catalytic cracking are typical of acid-catalyzed reactions. Tho-mas (Industrial and Engineering Chemistry, vol. 41, pages 2564-73 (1949)) has reviewed the known cracking catalysts and has shown that all of these will have acidic properties if certain structural conditions are fulfilled. The best known cracking catalysts are silica-alumina, silica-magnesia, silica- In addition to these, alumina-boria and titania-boria are known to be active cracking catalysts.

Although titania is often considered to be more or less equivalent to zirconia, since titanium and zirconium are members of the group IV-B elements of the periodic table, Thomas has shown that silica-titania compositions are not equivalent to silica-zirconia compositions as cracking'catalysts because titanium exhibits a different coordination number than does Zirconium in the solid structure of their respective oxides. Apparently, titanium always has a coordination number of six in its several oxides, while zirconium has a coordination number of eight in its one stable oxide. A six-coordinated oxide in combination with four-coordinated silica cannot exhibit strong acid properties according to the theory developed by Thomas and others.

Experience has shown that silica-titania compositions prepared by methods analogous to those employed in the preparation of silica-alumina, silica-magnesia, and silica-zirconia catalysts are indeed inactive as cracking catalysts under the conditions normally employed in commercial catalytic cracking. However, it has now been found that under hydrogen pressure silica-titania compositions exhibit extremely useful catalytic cracking properties. In fact, the cracking activity of such compositions under hydrogen pressure far exceeds that of the best known cracking catalysts employed in conventional catalytic cracking. Silica-titania compositions under hydrogen pressure appear to be equally as effective as silicazirconia compositions, which recently have been found to be far superior to silica-aluminia catalysts in the hydrocracking of high boiling refractory petroleum fractions.

It is also known that certain conventional cracking catalysts, e. g. silica-zirconia, or silica-alumina, may be composited with e. g. 5-20% by weight of certain hydrogenating components, notably the sulfides or oxides of certain transitional metals, especially those of chromium,

molybdenum, tungsten, iron, cobalt and nickel, and that the resulting composites are useful hydrocracking catalysts, i. e. for cracking in the presence of added hydrogen. Such conventional hydrogenating components, however, are excluded from the present invention, inasmuch as the hydrogenating activity obtained herein is apparently derived exclusively from the silica-titania composite itself, and not from any of the above types of known hydrogenating components. In fact, some of the known hydrogenating components are found to exert a deleterious effect.

It has been demonstrated in the past that cracking catalysts comprising silica in combination with alumina, magnesia or Zirconia, are without substantial hydrogenation activity at low pressures of hydrogen, since hydrogen acts merely as an inert diluent. Even at elevated pressures of hydrogen, a typical commercial silica-alumina catalyst exhibits little, if any, true hydrogenation activity in the decomposition of hydrocarbons. Silica-titania catalysts are similarly unknown as hydrogenation catalysts. The present invention is based essentially upon our discovery that the specific silica-titania composites described herein develop important and useful hydrogenating-cracking activity at high hydrogen pressures, e. g. above about 500 p. s. i. g. of hydrogen pressure. This characteristic sharply distinguishes the silica-titania catalysts from other known cracking catalysts such as silicaalumina, silica-magnesia, activated clays, and the like. The compositions found to be most useful for hydrocracking comprise those which contain between about 20% and 95% by weight of titania, and preferably those containing between about 50% and of titania, the remainder being essentially silica. However, it is not intended to exclude the presence oftrace amounts of impurities, such as the oxides or sulfides of metals such as iron, which may be associated with titanium salts as an impurity. Other group VIII or group VI metals may also be present, e. g. the oxides or sulfides of cobalt, nlckel, chromium, molybdenum or tungsten, but the proportion thereof in the finished catalyst should be less than about 0.5% by weight, based on the free metal. In the preferred modification, such extraneous metals are substantially or totally absent, i. e. less than 0.1% by weight 18 present.

In the preparation of is essential that the components be extremely intimately mixed, such as is achieved by coprecipitation of SiO and TiO For example, a catalyst prepared by dispersing very finely ground TiO (anatase) in sodium silicate, and adding acid to precipitate silica, was not active in the hydrocracking of a catalytic cycle stock. On the other hand, a catalyst of the same nominal composition prepared by adding sodium silicate solution to an HCl solution of TiC1 followed by exhaustive washing of the precipitate to remove sodium, was very active.

However, the catalysts may be prepared by any method which provides a sufliciently intimate association of the components. A molecular subdivision and distribution of the components in an amorphous, activated gel structure is preferred. Suitable methods for obtaining such composites include for example: (1) the impregnation of a hydrogel or adsorbent gel of one component with a solution or hydrosol of the other (or a compound decomposable thereto), followed by drying and calcining,

(2) coprecipitation of both components from a solu tion or solutions of soluble compounds thereof, followed by drying and calcining, or (3) co-trituration of the powdered dry components, hydrogels, or hydrous oxides,

preferably in the presence of a liquid fluxing medium, 7

followed by drying and calcining.

In the impregnation method, the titanium oxide may first be prepared, as for example by precipitation of the hydrogel from an aqueous solution of a soluble salt of i titanium. The hydrogel may be impregnated as such,

or after calcining to formfadsorbentTiO Suitable salts active silica-titania catalysts it for this purpose include for example titanium tetrachloride, titanium tetrafiuoride, titanium tetraiodide, titanium tetrabromide, titanium sulfates, or the like. The aqueous solution of the salt is treated with a stoichiometric excess of a suitable base, e. g., ammonium hydroxide, sodium hydroxide, potassium hydroxide or the like. The gelatinous precipitate of titanium hydroxide is filtered off, washed exhaustively with distilled water to remove any contaminating ions, and then dried and calcined at temperatures ranging between about 400 and 700 C. for 2-30 hours for example. The adsorbent oxide so prepared may then be impregnated with an aqueous solution of a soluble silicate, or a silica hydrosol. If silica hydrosol is employed, the impregnated material is merely drained, dried and calcined. If a soluble silicate, e. g., sodium silicate, is employed, the impregnated material is preferably leached with a weak acid such as acetic acid or aqueous CO in order to precipitate silica, and

. wash out the contaminating cation. The final composition is then dried and calcined for several hours at, e. g., 400 to 700 C.

Suitable titania gels for impregnation may also be prepared by alkaline hydrolysis of organic ortho-titanite esters, e. g., ethyl or methyl ortho-titanate with, e. g., aqueous ammonia.

Another method of impregnation comprises impregnating preformed hydrous or adsorbent silica gel with a soluble titanium compound. In this procedure an aqueous solution of any of the aforementioned titanium salts is prepared, the solution being sutficiently concentrated in titanium to give the desired proportion thereof in the finished catalyst. The silica gel is then immersed in the solution for several minutes, and drained of excess solution. The titanium is then precipitated in the pores of the adsorbent, dried and calcined at, e. g., 400 to 700 C. to obtain the finished catalyst. In some cases it may be difficult to obtain the desired proportion of titania in a single impregnation, and in such cases the impregnation is repeated after drying or calcining, until the desired titania content is obtained.

In the co-trituration procedure a preformed titania gel is intimately ground together with a silica hydrogel, either in the presence or absence of a moistening agent, and the intimately admixed solids are then subjected to calcining temperatures.

It has been observed that, while the catalysts prepared by the above impregnation methods are moderately active, they are considerably less active than nominally similar compositions prepared by coprecipitation. In coprecipitation processes, an aqueous solution may be formed containing the desired ratio of soluble titanium and silicon compounds. A third reagent is then added which etfects precipitation of both components, preferably as hydrous oxides, but possibly as other insoluble compounds which are convertible to the oxides upon subsequent treatment, as by calcining. For example, an aqueous solution of sodium silicate and sodium hydroxide may be poured rapidly with stirring into an aqueous solution of HCl and titanium tetrachloride, whereupon a co-precipitate of silica gel and hydrous titanium oxide is formed. This mixture is then fiiltered and the precipitate washed exhaustively and calcined. Some composites of silica-titania may contain considerable amounts of zeolitic or strongly adsorbed sodium ion which is detrimental to catalytic activity and stability. It may be desirable in these cases to remove sodium before calcination by base-exchanging with ammonium ion or hydrogen ion.

In another coprecipitation process, an organic orthotitanate ester may be dissolved in an organic orthosilicate and the mixture subjected to hydrolysis with an aqueous alkali, e. g., ammonium hydroxide, sodium hydroxide, etc. The mixture may be heated and agitated to hasten the hydrolysis. The precipitated hydrous oxide mixture is then filtered off, washed if necessary to remove alkali metals, dried and calcined.

A specific coprecipitation method which is highly economical involves dissolving a commercial pigment grade anatase or rutile (substantially pure TiO in the requisite amount of aqueous hydrofluoric acid, and mixing this solution with one of alkali silicate plus excess alkali. The excess alkali is preferably ammonia, as this minimizes the problem of sodium contamination.

In still another coprecipitation method, a blend of titanium tetrachloride and silicon tetrachloride is prepared corresponding to the desired TiO /SiO ratio. This blend, or a blend of otherhalides of silicon and titanium,

is then added slowly, with cooling if necessary, to suificient of an aqueous ammonia solution "to convert substantially all of the halides to hydrous oxides, resulting in a final mixture having a pH of preferably about 6 to 8. The hydrous oxides are filtered and washed to remove most of the associated ammonium chloride. Alternatively the washing step may be omitted if in the subsequent calcining step the volatilization of the ammonium chloride is not bothersome. The oxides are then dried, calcined, and pelleted in the usual manner. This method completely avoids the introduction of unwanted non-volatile cations into the composition. This objective may also be achieved in analogous preparations wherein an equivalent amount of hydrofluosilicic acid is substituted for the silicon tetrachloride. Also the titanium halide employed may be a hydrofluoric acid solution of anatase or other forms of TiO- Suitable mixed halides in solution may also be prepared by treating a mixture of purified titania (anatase) and silica with a slight excess of aqueous hydrofluoric acid, and the resulting solution precipitated with ammonia. Alternatively, a hydrofluoric acid solution. of TiO-,, may be blended with a preformed solution of hydrofluosilicic acid, and precipitated with ammonia.

In any of the above precipitation methods, the ammonia may be substituted by other bases such as ammonium carbonate, sodium hydroxide, sodium carbonate, sodium bicarbonate, potassium hydroxide and the like. Nonvolatile cations may be removed from the hydrous gels by extensive washing With distilled Water, preferably after first leaching with ammonium chloride, ammonium sulfate or ammonium nitrate solutions or the like to effect base-exchange with any tightly bound alkali metal ions.

The above-described coprecipitation procedures are 7 found to produce catalysts which are in general markedly more active than the less homogeneous catalysts prepared by other methods such as impregnation or cotrituration. Maximum activity is obtained, moreover, when the coprecipitation is carried out under conditions favoring the simultaneous precipitation of both components in gel form, i. e. under conditions which will prevent one component from precipitating appreciably before or after the other. This is somewhat of a problem when employing titanium halide solutions inasmuch as these salts tend to hydrolyze; if suflicient excess acid is present to prevent hydrolysis, the silica gel will tend to be precipitated first upon addition of alkaline silicates, and if insufficient excess acid is present, titania gel may tend to precipitate ahead of SiO This problem can be overcome to some extent by first dissolving the titanium halide in a small volume of the concentrated halogen acid, e. g. 37% HCl, or a small volume of water, and then diluting the concentrated solution with water. This procedure is found to allow the formation of a homogeneous mixed hydrosol, upon addition of sodium silicate, which rapidly sets to a clear and homogeneous mixed hydrogel. This procedure is illustrated by the following example:

Example I A. An attempt to prepare a hydrogel containing silica and titania was made by dissolving 24 grams of TiCl, in 500 ml. of water and adding thereto 1225 ml. of a sodium silicate solution repared by diluting 225 mi.- N Brand sodium silicate (containing 0.40 gram of SiO; and 0.124 g. Na O per ml.) with 1000 ml. of H 0. When the TiCl was added to the above quantity of water, precipitation occurred and the final hydrogel was very heterogeneous in appearance. The addition of 35 ml. of concentrated (37% HCl to the TiCh-water mixture did not produce a homogeneous solution.

B. 25 grams of TiCh was added slowly to 35 ml. of concentrated (37%) HCl, forming a yellow, entirely homogeneous solution. When this solution was diluted with 500 ml. of water the resulting solution was completely clear and water-white. Addition of the same quantity of sodium silicate solution as used in Example IA produced a clear hydrosol which rapidly set to a clear and homogeneous hydrogel, containing about 90% by weight SiO and of TiO:,,. After washing free of chloride and drying, the catalyst granules were hard and glassy, similar in appearance to silica gel, showing that the titania was uniformly dispersed in the structure.

it is also possible to prepare an aqueous solution of TiCh, which is stable on dilution, without using additional HCl. If the TiCL; is diluted first with a limited quantity of water (l2 times the volume of Ticl the initially precipitated products of hydrolysis will go back into solution, and the resulting clear homogeneous solution is stable toward infinite dilution for a considerable period of time.

Other methods favoring simultaneous coprecipitation include using preformed silica hydrosols in conjunction with acidic titanium halide sols or solutions. Also alkaline titanate or pertitanate sols or solutions may be admixed with alkaline silicate solutions, and the mixtures acidified to produce mixed hydrogels.

In any of the above preparation methods, the composite may be formed into pellets or granules at various stages in the manufacture. The moist powders may be compressed or extruded to form pellets prior to calcining, or the calcined powdered gels may be compressed to form the desired pellets. Ordinarily it is desirable to employ the catalyst in the form of pellets or granules ranging in size from about /8 inch to A2 inch in diameter. In forming such pellets it may be desirable to employ minor proportions of binders such as hydrogenated corn oil or the like, and in case the dry materials are to be pelleted, a small proportion, e. g. 12% by Weight, of graphite may be incorporated therein to act as a lubricant. The binders and lubricants, if employed, are removed by combustion during the final calcining. Those skilled in the art will readily appreciate that other compounding and pelleting procedures may be employed.

The above catalysts may be utilized for hydrocraclcing a great variety of mineral oil feed stocks, which are generally high boiling fractions derived from petroleum stocks or shale oils. The catalysts are especially useful for hydrocracking refractory cycle stocks from conventional cracking operations, or alternatively they may be used for hydrocracking virgin gas oils to prevent the buildup of refractory residues from the cracking operation. Any of these feed stocks may also contain organic sulfur in amounts up to about 4% by Weight, and organic nitrogen in amounts up to about 1% by weight. In the hydrocracking process these sulfur and nitrogen compounds are largely decomposed.

Example 11 In order to determine the non-hydrogenative cracking activity of SiO -TiO catalysts, the catalyst composite of Example l-B was tested in a very sensitive test for acid-type cracking, viz., the dealkylation of isopropylbenzene to propylene and benzene. The test conditions were: 500 C., L. H. S. V=l, and atmospheric pressure. In one hour of processing a total of 50 ml. of gas was produced. Under the same conditions a commercial 7 silica-alumina cracking catalyst containing about 85-90% All gravity at 60 F degrees 21.3 ASTM distillation end point F 673 Vol. percent 400 F. end-point gasoline 2.1 Wt. percent sulfur 0.92 Wt. percent nitrogen 0.14 Vol. percent aromatics 62 Vol. percent olefins 5 Vol. percent saturates 33 The processing conditions employed were as follows:

Temperature 900 F.

Pressure 1000 p.s 1 g L. H. S.V 0.5.

H /liquid feed 8000 s. c. f. per barrel.

Length of runs 6 hours.

Example II A catalyst comprising 85% by weight of pure SiO and 15% pure "B0 was prepared by dissolving 45 grams of a mixture of methyl and ethyl orthotitanates in 278 grams of ethyl orthosilicate. This solution was poured into 1000 ml. of water containing 25 ml. of 28% ammonia solution, and the mixture was heated to complete the hydrolysis of the esters. The precipitated hydrous oxide mixture was filtered out, dried, pelleted, and calcincd.

Processing of the cycle stock over this catalyst resulted in the production of 18% by volume of 400 F. endpoint gasoline and 69% of a heavier fraction, giving a selectivity of gasoline production of 58%. This result is essentially the same as that produced by pure silica gel, showing that 15% TiG is not an effective amount. The selectivity factor as employed herein is defined as the ratio of gasoline yield to the volume-percent of feed not recovered as high boiling residue:

Example IV A catalyst comprising 75% by Weight of SiO and 25% TiO was prepared by dissolving 216 grams of an HCl-TiCh solution, containing the equivalent of 50 grams of TiO in 1300 ml. water, cooling to 10 C., and adding with vigorous stirring a cooled solution of 523 grams of N Brand sodium silicate (150 g. SiO plus ml. of 28% ammonia solution diluted to 1500 ml. This resulted in a slurry of gelatinous coprecipitate having a pH of 7. The slurry was filtered, partially dried, Washed free of chloride, dried, pulverized, pelleted, and calcined.

Under the above-described processing conditions, this catalyst produced 33% by volume of 400 F. end-point gasoline and 61% of a heavier fraction, giving a selectivity of gasoline production of The sulfur content of the total liquid product was 0.35% by weight and the nitrogen content was 0.05%. This example shows that 25 of Ti0 is fairly effective for hydrocracking.

Example V A catalyst comprising 50% by weight of SiO and TiQ was prepared by diluting to 1500 ml. an HClliCh solution containing the equivalent of 75 grams of TiO,, and adding to this with vigorous stirring a solution of 188 ml. of N Brand sodium silicate (75 grams of SiO plus 144 grams of NaOH dissolved in 1500 ml. of water. The resulting'gelatinous slurry, having a pH of 7, was filtered, partially washed, then partially dried, and washed completely free of chloride ion. The filter cake was then dried, pulverized, pelleted, and calcined.

A yield of 55% by volume of 400 F. end-point gasoline and 40% of a heavier fraction was obtained from the cycle oil with this catalyst, giving a selectivity of gasoline conversion of 92%. The sulfur content of the total liquid product was 0.10% by weight and the nitrogen content 0.02%. The gasoline was found to have a leaded (3 ml.) research octane rating of 98, which is considerably higher than the octane rating of gasolines produced by conventional catalytic cracking of similar charge stocks.

Example VI A catalyst comprising 10% by weight of SiO- and 90% Ti was prepared by dissolving 310 ml. of pure TiCl, (equivalent to 225 grams of TiO in 400 ml. of cooled water, diluting to 15001111., and adding to this solution with vigorous stirring a solution of 62.5 ml. of N Brand sodium silicate (25 grams of SiO in 750 ml. of 28% ammonia diluted to 2000 ml. The pH of the resulting slurry was 7. The slurry was filtered, partially washed, partially dried, and then washed completely free of chloride ion. The washed product was air dried at 25 C., pulverized, pelleted, and calcined. A yield of 54% by volume of 400 F., end-point gasoline and 31% of a heavier fraction was obtained from the cycle stock with this catalyst, giving a selectivity of gasoline production of 78%. The sulfur content of the total liquid product was 0.16% by weight, and the nitrogen content 0.03%.

It should be noted that in each of the Examples IV, V and VI, the heavy unconverted feed residue had an A. P. I. gravity of between about 18 and 20, indicating good recycle characteristics.

Example VII A catalyst comprising 100% TiO was prepared by adding 276 ml. of purified TiCl, to 375 ml. of cooled water, diluting the resulting homogeneous solution to 2000 ml. with water, and precipitating hydrous TiQ by the addition of 725 ml. 28% ammonia to give a pH of 7. The precipitate was filtered, partially dried, washed free of chloride ion, dried, pulverized, pelleted, and calcined 18 hours at 900 F.

Processing of the cycle oil over this catalyst under the previously described conditions resulted in a 25% volumetric yield of gasoline and 69% of a heavier fraction, giving a selectivity of gasoline formation of 80%. Thus, pure titania has only a very moderate intrinsic hydrocracking activity as compared to silica-promoted titania catalysts.

Example VIII The catalyst of this example serves to show that intimate interaction between SiO and TiO is necessary to produce an active hydrocracking catalyst, and inferentially shows that pure Ti0 (supported on SiO is also inactive as a hydrocracking catalyst.

A catalyst comprising 50% by weight of Si0 and 50% TiO was prepared by dispersing 100 grams of C. P., finely divided Ti0 (anatase) in 250 ml. of N Brand sodium silicate (100 grams of SiO;) diluted to 2500 ml., and precipitating silica in the presence of the TiO,, by addition of 360 ml. of 2.5 N HCl. A solid hydrogel, having a pH of 7.5, was formed in which the TiO;, was evenly dispersed. The hydrogel was crushed, pressed free of excess solution and partially dried. The product was redispersed in water and washed completely free of chloride ion. Then it was dried, pulverized, pelleted, and calcined.

Processing of the cycle stock over this catalyst pro duced a 21% volumetric yield of 400 F. end-point gasoline and 65% of a heavier fraction, giving a selectivity of gasoline production of 60%. The sulfur con tent of the total liquid product was 0.63% and the nitrogen content 0.13%.

Example IX Example X A conventional silica-alumina (88% SiO 12% A1 0 was employed in the conversion of the cycle stock under the conditions above outlined. The yield of gasoline was 21% by volume of the cracking catalyst charge, which yield is about what would be obtained in the absence of hydrogen. The selectivity of gasoline make was 60%. The sulfur and nitrogen contents of the total liquid product were, respectively, 0.71% and 0.06%, confirming the conclusion, based on the yield of gasoline, that silica-alumina catalysts are inelfective hydrogenation catalysts as compared to silica-titania catalysts. (The decrease in nitrogen content is due to strong adsorption on the catalyst.)

Example XI The recycle stock was processed under the conditions outlined in Example I but in the absence of a catalyst, quartz chips being used to fill the reaction chamber. A conversion of 10% by volume of the charge to 400 F. end-point gasoline and an 83% recovery of the higher boiling fraction were obtained. The sulfur and nitrogen contents of the total tively, 0.72% and 0.14%. results obtained herein are liquid product were, respec- This example shows that the catalytic and not thermal.

Example XII In order to compare the above results with those obtainable from a known catalyst having high hydrogenation activity, a 2.9% C0D, 8.3% M00 84.4% Alp -4.4% Si0 catalyst was evaluated under exactly the same conditions. A yield of 32% by volume of gasoline and a recovery of 40% of a heavier fraction having an A. P, I. gravity of 18.1 were obtained. Thus, not only a lower activity is exhibited by this catalyst as compared to the catalyst of Example IV, but the selectivity of 53% is the poorest of any catalyst tested.

From the above examples it will be apparent that the catalysts described herein exhibit surprisingly high activity for the hydrocracking of refractory cycle stocks and other heavy oils to produce high yields of highoctane gasoline and good desulfurization and denitrogenation of such oils. The essential requirement as to thecatalyst appears to be that it shall comprise as essential active components, silica and titania in active, intimate association. It is not intended that the invention should be restricted to the details disclosed in the examples or elsewhere, since many variations may be made by those skilled in the art without departing from the scope or spirit of the following claims.

We claim:

1. A process for hydrocracking a mineral oil feed stock boiling above the gasoline range to produce gasoline-boiling range hydrocarbons which comprises s. c. f. of hydrogen per barrel of feed, and under hydrocra'cking conditions, said hydrocracking catalyst comprising as essential active ingredients coprecipitated titanium oxide and silicon oxide in intimate admixture, the TiO /SiO ratio in said catalyst being between about 95/5 and 20/80 by weight, said hydroeracking conditions comprising temperatures between about 750 and 1050 F., hydrogen pressures between about 500 and 5,000 p. s. i. g., and space velocities between about 0.1 and 10.0 volumes of liquid feed per volume of catalyst per hour.

2. A process as defined in claim 1 wherein said feed stock is a highly aromatic residual oil from a cracking operation conducted in the absence of added hydrogen.

3. A process as defined in claim 1 wherein the TiO /SiO ratio in said catalyst is between about 50/50 and 90/10 by weight.

4. A process as defined in claim 1 wherein said catalyst is prepared by coprecipitation of the hydro-us oxides of titanium and silicon from aqueous solutions of soluble compounds thereof, followed by drying and calcining of the mixed hydrous oxides.

5. A process as defined in claim 1 wherein said catalyst is at least about 99.5% by weight SiOTiO 6. A process for hydrocracking and desulfurizing a mineral oil feed stock boiling above the gasoline range and containing at least about 0.1% sulfur in the form of organic sulfur compounds to produce gasolineboiling range hydrocarbons of reduced sulfur content which comprises contacting said feed stock with a hydrocracking catalyst in the presence of between about 1000 and 10,000 s. c. f. of hydrogen per barrel of feed, and under hydrocracking conditions, said hydrocraclting catalyst comprising as essential active ingredients coprecipitated titanium oxide and silicon oxide in intimate admixture, the TiO /SiO ratio in said catalyst being between about 95/5 and 20/ 80 by weight, said hydrocraclting conditions comprising temperatures between about 750 and 1050 F., hydrogen pressures between about 500 and 5000 p. s. i. g., and space velocities between about 0.1 and 10.0 volumes of liquid feed per volume of catalyst per hour.

7. A process as defined in claim 6 wherein said feed stock is a residual oil rich in fused-ring aromatic hydrocarbons and is obtained as residue from a catalytic cracking operation conducted in the absence of added hydroi2 gen at a temperature hetween'about 800 and 1000 F. 8. A process as defined in claim 6 wherein said feed st'oclt. is a residual oil rich in fused-ring aromatic hydrocarbons and is obtained as residue from a thermal cracking operation conducted in the absence of added hydrogen as a temperttire between about 850 and 1050 F.

9. In the preparation of mixed silica gel-titania gel catalysts wherein titanium tetrachloride is added to a large volume of water sullicient normally to produce a visible precipitate of hydrolyzed titanium tetrachloride, and the resulting suspension-solution is then mixed with aqueous alkaline silicate to form a coprecipitated silicatitania composite, the improvement which comprises avoiding the formation of insoluble hydrolyzed titanium tetrachloride prior to the addition of silicate by first diluting said titanium tetrachloride with a small volume of solvent, insuiiicient to cause visible precipitation, said solvent being selected from the group consisting of water and aqueous hydrochloric acid, stirring without further addition of solvent until a clear homogeneous solution is formed, then diluting the resulting solution with a large volume of water to form a relatively stable sol without visible precipitate, rapidly mixing said sol with aqueous alkaline silicate to form a transient mixed hydrosol, allowing said mixed hydrosol to stand until a homogeneous mixed hydrogel of silica and titania is formed, and washing, drying and calcining said mixed hydrogel.

10. A catalyst consisting essentially of between about 20% and 95% by weight of titania gel-and between about and 5% of silica gel, said catalyst being in the form of an intimately and simultaneously precipitated co-gel prepared by the method of claim 9.

References Cited in the tile of this patent UNITED STATES PATENTS 2,253,787 Melaven Oct. 14, 1941 2,378,290 Drake lune 12, 1945 2,500,197 Michael Mar. 14, 1950 2,656,304 MacPherson Oct. 20, 1953 2,670,321 Morrell Feb. 23, 1954 2,703,308 Oblad Mar. 1, 1955 OTHER REFERENCES Serial No. 390,534, Pier (A. P. 0), published May 18, 

1. A PROCESS FOR HYDROCRACKING A MINERAL OIL FEED STOCK BOILING ABOVE THE GASOLINE RANGE TO PRODUCE GASOLINE-BOILING RANGE HYDROCARBONS WHICH COMPRISES CONTACTING SAID FEED STOCK WITH A HYDROCRACKING CATALYST IN THE PRESENCE OF BETWEEN ABOUT 1000 AND
 10. 000 S. C. F. OF HYDROGEN PER BARREL OF FEED, AND UNDER HYDRECRACKING CONDITIONS SAID HYDROCRACKING CATALYST COMPRISING AS ESSENTIAL ACTIVE INGREDIENTS COPRECIPITATED TITANIUM OXIDE AND SILICON OXIDE IN INTIMATE ADMIXTURE THE TI02/SI02 RATIO IN SAID CATALYST BEING BETWEEN ABOUT 95/5 AND 20/80 BY WEIGHT, SAID HYDROCRACKING CONDITIONS COMPRISING TEMPERATURES BETWEEN ABOUT 750* AND 1050*F., HYDROGEN PRESSURES BETWEEN ABOUT 500 AND 5,000 P. S. I. G., AND SPACE VELOCITIES BETWEEN ABOUT 0.1 AND 10.0 VOLUMES OF LIQUID FEED PER VOLUME OF CATALYST PER HOUR. 